A reduction gearbox generally includes a box body and a cover, and shaft holes for allowing an output shaft to pass therethrough are provided on both the box body and the cover. Since the box body and the cover are two independent components, the shaft hole of the box body and the shaft hole of the cover are machined separately. Therefore, high requirements are proposed on the machining process, the time for machining is long, and the high-precision coaxiality of the shaft hole of the box body and the shaft hole of the cover cannot be guaranteed.